Web API 中的音频 Context.close()

Web 音频 API 有助于使网站应用程序的音频听起来正确。声音使网站更加有趣和有吸引力。使用音频 API，可以构建许多音乐或声音应用程序。在本文中，我们将了解audiocontext.close()以及有关音频 API 的一些基本信息。

音频上下文是一个对象，用于对网站或应用程序的音频进行各种操作。这是一个预先构建的函数，可用于各种浏览器，如 google 和 Firefox。在更改任何音频之前，必须存储音频源。有 3 种主要类型的音频源。

• 振荡器：用于产生数学计算的声音
• 音频样本：从各种文件中获取音频
• 音频流：从网络摄像头或麦克风获取音频

使用任一来源流式传输音频后，您可以使用不同的节点来强调或减弱音频的部分。执行完节点功能后，将音频连接到目的地，然后播放声音。一些不同的节点是 Filter、ChannelSpiltterNode、AudioWorkletNode 等……

AudioContext.close（）：该音频上下文函数可以关闭audiocontext，从而分离与audiocontent相关联的任何硬件资源。即该函数不会进一步接受/给予声音设备的任何输入。但是在使用 close() 之前已经存储的音频可以被操纵。这在移动设备等低功耗设备中非常有意义。如果音频上下文停留在设备的资源上，则保持开启，从而导致断电。

句法：

// Declaring audiocontext constrcutor
var audioContext=new AudioContext();
audioContext.close().then(function()
     {.
      .
      . });
await audioContext.close()

示例：在以下代码中，创建了一个带有 3 个按钮的小型 HTML 页面。单击每个按钮执行与音频相关的相应功能。在该示例中，可以开始和停止音频，即恢复。请注意，恢复与停止不同，因为恢复音频意味着暂时暂停音频并从停止的位置重新开始。而使用 close() 停止音频会从声音设备中完全删除音频并将状态设置为开始状态。

Javascript

    
        
  
        states
  
        
        
            body {
                background: lightcoral;
                color: #323232;
                font-weight: 300;
                height: 100vh;
                margin: 0;
                display: flex;
                align-items: center;
                justify-content: center;
                text-align: center;
                font-family: Helvetica neue, roboto;
            }
            .button:hover {
                background-color: aquamarine;
            }
            .btn-group .button {
                background-color: bisque;
                border: 1px solid black;
                color: black;
                padding: 15px 32px;
                text-align: center;
                text-decoration: none;
                font-size: 16px;
                cursor: pointer;
                width: 150px;
                display: block;
                margin: 4px 2px;
            }
            .button:hover {
                background-color: whitesmoke;
            }
  
            h1 {
                font-weight: 200;
                font-style: 26px;
                margin: 10px;
            }
        
    
  
    
        
            
              Start Audio
            
            
              Suspend Audio
            
            
              Stop Audio
            
              
Current context time: No context exists.
  
        
  
        
            let AudioContext;
  
            const start = document.getElementById("start");
            const susres = document.getElementById("sus");
            const stop = document.getElementById("stop");
  
            const timeDisplay = document.querySelector("p");
  
            susres.setAttribute("disabled", "disabled");
            stop.setAttribute("disabled", "disabled");
  
            start.onclick = function () {
                start.setAttribute("disabled", "disabled");
                susres.removeAttribute("disabled");
                stop.removeAttribute("disabled");
  
                // Create web audio api context
                AudioContext = window.AudioContext 
                      || window.webkitAudioContext;
                AudioContext = new AudioContext();
  
                // Create Oscillator and filter
                const oscillator = AudioContext.createOscillator();
                const filter = AudioContext.createBiquadFilter();
  
                // Connect oscillator to filter to speakers
                oscillator.connect(filter);
                filter.connect(AudioContext.destination);
  
                // Make audio/noise
                oscillator.type = "sine";
  
                // hertz frequency
                oscillator.frequency.value = 100; 
                oscillator.start(0);
            };
  
            // Suspend/resume the audiocontext,i.e,
            // the audio can be played back
            susres.onclick = function () {
                if (AudioContext.state === "running") {
                    AudioContext.suspend().then(function () {
                        susres.textContent = "Resume Audio";
                    });
                } else if (AudioContext.state === "suspended") {
                    AudioContext.resume().then(function () {
                        susres.textContent = "Suspend Audio";
                    });
                }
            };
  
            // Close the audiocontext,i.e, the audio is
            // completely stopped after the stop button 
            // is clicked by promise the audio resets 
            // the response to beginning state(Create Audio)
            stop.onclick = function () {
                AudioContext.close().then(function () {
                    start.removeAttribute("disabled");
                    susres.setAttribute("disabled", "disabled");
                    stop.setAttribute("disabled", "disabled");
                });
            };
  
            function displayTime() {
                if (AudioContext && AudioContext.state !== "closed") 
                {
                    timeDisplay.textContent = "audio time "
                    + AudioContext.currentTime.toFixed(3);
                } 
                else 
                {
                    timeDisplay.textContent = "Context not started";
                }
                requestAnimationFrame(displayTime);
            }
  
            displayTime();
        
    

输出：音频通过单击“创建音频”开始，音频可以通过“暂停音频”暂时停止，然后在没有时间间隔“恢复音频”的情况下再次开始。使用 Audiocontext.close() 通过“停止音频”停止音频